hansell



Dec. 5, 1933. C, W, HANSELL 1,938,331

CATHODE RAY TUBE DETECTOR CIRCUITS Filed Jan. 14, 1930 INVENTOR CLARENCEW. HANSELL ATTORNEY Patented Dec. 5, 1933 CATHGDE RAY TUBE nn'rnc'ronCIRCUITS Clarencel W. Hansell, lort Jefferson, Long Island,

Y., assigner to Radio Corporation vci? America, a cerporation ofDelaware Application January 14,

13 Y claims.

' My present invention relates to detectors,` and more particularly todetector circuits embodying a space discharge device oi the cathode raytype,

the detector circuit being such that the output is much less affected byundesired emission variations than the circuits now in common use.v

In my copending application Serial Number 418,281 filed January 3,.1930, there has been disclosed a method of, and means for, eliminatingtube noises in the iinal output of high frequency energy ampliers, itbeing there explained that such tube noises occur because of actualirregularities in the rate of emission of 'electrons from the tubecathode, the method disclosed permiting greater radiofrequencyamplification to be used so that smaller values of radiofrequency energy can be amplified successfully. Briefly, the saidcopending application discloses an ain.- plier circuit which comprisesan electron discharge device of the cathode ray type including,

a cathode, a plurality'of 'anodes electrostatically shielded from thecathode, the anodes being connected in such a manner that variationsinemisf sion from the cathode result in equal and opposite variations inthe anode output circuit whereby the disturbing anode currents balanceout and no noise is present in the output ofthe amplier.

Now, I have found that the novel cathode raycathode or any variations inanode and control electrode power supply potentials will result inopposite variations in the said anode circuit, with the result that lesstube noise Will be impressed upon the input of subsequent stages ofaudio amplification. Another important objectof the present invention isto provide a circuit for detecting amplitude modulation of a carrierwave of high frequency, which circuit includes a cathode ray tube,comprising an electron emission source, and a plurality of anodeselectrostatically shielded from the said source,` the anodes beingconnected in such a manner that variations in emission from the saidsource will result in opposite variations that any variations inemission from the tubeiea. serial. No. 420,651

(ci. 25a-2p in the anode output circuit whereby the currents which,result from the emission variations will balance out and less noise bepresent in the audio output of the detector circuit.

- Still another object of the invention is to pro'- vide a cathode raytube capable of sensitive detection of amplitudemodulated carrier Waveswhen arranged in a .detector circuit connected for eliminating noises`due to variations in cathode emission, `which tube includes a cathode,a pair of anodes electrostatically shielded from the cathode, all pointson the ,cathode being substantially equi-distant from the two anodes,and one or more control electrodes symmetrically dis-` posed withrespect to the anodes and cathode and causing deflections in theelectron stream, the input circuit of the tube'being so arranged thatamplitude modulated carrier waves impressed thereon are readilyrectified. f l

Other objects'of the invention are to improve generally the eiciency ofdetector circuits ,emi bodying electron discharge devices, vand to,further, provide an electron discharge tube acting as a detector whichis durable and reliable in opera'- tion,` possesses a high usefuldetection range, a minimum of the action from the output circuit. backto the input circuit, and maybe readily arranged in a detector ,circuitVvto reduce tube noises arising from irregularities in cathode emission.v l f 8,5

The novel features which I believe to be char acteristic of my inventionare'set forth in particularity in the appended claims, the inventionitself, however, as to both its organizationand method of operation willbest be understood by reference to the following description takeninconnection with the drawing in which I have indicated diagrammaticallyseveral circuit organizations whereby my invention may be `carried intoeffect.

In the drawing, Fig. 1 diagrammatically shows a cuit embodying theinvention,l

Fig. 2 is a diagrammatic representation of a modified form ofdetectorcircuit.

Referring to the accompanying drawing, in which like characters ofreierence'indicate the same parts in the diiierent ligures, there isshown in Fig. 1 a cathode ray tube detector circuit for detectingamplitude modulation of a carrier 105 wave, having its tunedinputcircuit 1, 2 coupled, as at M', to a source of amplitude modulatedradiofrequency energy, the latter being generally designated as modulatedradioinput. The, output circuit of the tube-includes the primaryof .an110 detector ciraudio transformer A having a pair of series cony nectedcapacities 4, i connected in shunt therewith, the connection between thecapacities being tapped, vas at point 5, and grounded for shortcircuiting radio frequency components of current in lthe anode circuits.v

The secondary 6 of the audio transformer A f may be connected to anyutilization circuit, gen-V for the reason that the tube has been sodescribed.

in the aforementioned copending application, but will brieiiy explainsuiicient of the structure to enable the present detector circuit to bermore fully understood. The tube consists of three insulating sections5', 6 and 7. Section 5' has Vsealed in it` the cathode or filament 8,the latter being heated by a Vsource of current A. A pair of anodes 9, 9are disposed adjacent an opening'ininsulating section 7, the saidopening being closed by a screen grid or electrostatic shielding member10. The shieldlO is retained in parallelism with the anodes 9, 9 by ametal cylinder-1l, the latter havingits opposite ends sealed toinsulating sections 6' and '7. A second metal cylinder 12, has itsopposite ends sealed to insulating sections 5 and-6. A pair of wires.13, 13 having the greater portionof their length substantiallyparallel, are sealed to the section 5 at an end thereof. Y

In order to mount the tube an annular, metallicmounting and shieldingmember 14 is pro'- vided, the latter member contacting with the Yexterior of the metal cylinder 11, the member 14 being 'shown for thesake of simplicity as a single line, it being understood that thisstructure is described in detail in my aforementioned copendingapplication.. This shielding member 1li, when the tube is in operation,serves to cover the opening between two shielded compartments containingthe Vinput and output circuits Yso that there is noreaction fromtheoutput circuit back into the input circuit 'due to electrostatic orelectromagnetic coupling. f

' The two anodes 9 and 9' are electrostatically shielded fromall otherparts Within the Vtube by the shield grid 10. The two control electrodes13, 13 are symmetrically spaced with respect to the anodes and filamentl8, it being understoodY that only one control electrode can be'employed,if desired. The filament 8, furthermore, is designed with a relativelylarge surface area; .a low heating temperature is preferably used to.minimize, atV thez beginning, the amount of emission variation,1theeffects of. which it is desired tol in their effect on the two anodes'.v

I will now describe the connections between the tube, the tuned inputcircut,.and the output circuit -which will reduce noise resulting fromvariations in'cathode emission, and which'will permit more variations inplategand. grid power supply voltages. Positive potential is applied tothe screengrid 10 and the anodes 9 and 9 for the tube from currentsources Dv and B respectively. The positive terminal of the source B isconnected by a lead 15 to the midpoint of inductance coil 3.

YA lead 16` connects the Vpositive terminal of source D to theshieldingmember 14. The l'ament heating source A has shunted across it aby-pass condenser 20. the positive terminal of Y the source and one leadof the iilament being grounded, it being also observed that one terminalof the condenser 20 is also grounded.

One of the control electrodes 13' is connected to the high potentialside of the tuned input circuit 1, 2 and is negatively biased from asource C through a lead 25. The other control electrode 13 Ais connectedto the positive-terminal of the source C by a lead 26, it being observedthatthe ele"- trode 13 is connected to the cathode lead of the filamentthrough a kcapacity 21. The metallic cylinder l2khas negative potentialapplied to it, for concentrating the electronic stream issuing from theiilament 8, by means of a lead 19 connected between the negativeterminal of source E and the cylinder. The low potential side of thevariable condenser 2 in the input circuit of the tube is groundedthrough a capacity 22.

I have represented the electronic stream issuing from the cathode orlament 8 by means of a series of dotted lines 30 passing betweenthecontrol electrodes 13 and 13'. The middle of these lines shows .the meanposition which the stream is made to take when the input circuit hasenergy from the transmitter carrier wave impressed on it, but thiscarrierl is not being. modulated. As soon as the incoming carrier ismodulated the mean position Yof the stream is varied in accordance withthe modulation, and a differential variation is set up in the' currentsto theanodes 9 and9` resulting in a current corresponding* to themodulation in the outputcircuit 6.

The reason for the variation in the mean position of the electronstream, which results in the useful output, is that therpull on theelectrons in v the stream varies notonly vwith the potential' of Thedisplacement causes the pull on the stream l to increase andthia inturn, increases the displacement. When the electrode 13 has a negaitstive radio frequency potential, it repels the stream Y (or attracts itless), and the stream is displaced away from the electrode.

In this case, however, the displacement reduces the force and theUtotaldei'lection is therefore lessthanwouldv be caused by an equalpositive swing on electrode 13. It is also to be noted that an increasein vradio frequency potential on the control electrode increases thedeflection of the streamtoward the electrode'rnore rapidly than it'increases the deection away from the electrode.

'A decrease in radio frequency potential Ydecreases the deiiectiontoward the electrode faster than it decreases the deection away from it.The result is avariation in the mean position of the electron stream 'inaccordance with the modulation, and this causesv the differentialvariation in the currents to the two anodes 9 and 9 producing a usefuloutput from the tube which is substantially a copy of the modulationwhich isto be detected. Thisfo'rrn of detection corresponds closely tothe detection which may be obtained'from the ordinary type of Vacuumtube due to its asymmetrical grid voltage-plate current characteristic.y

In Fig. 2, I have shown aA modified form' of detector circuit employinga cathode -ray tube in which the circuit elements, similar to those inVFig'l are designated by the same reference nul merals. In this circuit,it will be noted that the input and output circuit are the same as inFig. 1, with the exception that a leak resistance R is connected betweenthe tuned input circuit 1, 2 and the negative terminal of battery Cthrough lead 25,

Again, the metal cylinder 12 is negatively biased-from ra source 31which is connected through a lead 19 to the negative terminal of thebattery B. The control electrode 13, instead of being connected to thepositive terminal of batteryC, as in'lig. 1, is connected to lead 19,thus being positively biased by the source 3l with respect to cylinder12, but negative with respect to electrode 13 and cathode 8. However, itis to be noted that the values and polarities of the potentials appliedto the electrodes by the sources B, C, D, E and 3l may be variedaccording to the design of the tube and conditions under which it isoperated.

It will be further noted that the filament circuit includes a batterysource A which has connected in shunt therewith a pair of seriesconnected radio frequency by pass condensers 40', the

connection between which condensers is grounded. TheV midpoint ofsource-A is connected by a lead el to the positive terminal of sourceC.`

This modied form of detector circuit depends for its action upon therectification of radio frequency energy through electrode 13 whichcauses a unidirectional component of current to flow through theresistance R the value of which varies with the amplitude or modulationof the J carrier wave which is to be received. This variableunidirectional current causes the average potential of electrode 13 tovary in accordance with the modulation, and this variation in potentialcauses a deflection in the mean position of the electron stream so as todifferentially vary the currents to anodes 9 and 9. This gives an outputfrom the tube which is substantially a copy of the modulation which isto be detected. The action of the resistance R in this case is quitesimilar to that of the grid leak in the commonv type of detector.

It will thus be seen that I have discovered a new method, and devisednovel means for reducing tube noises in the output circuits ofdetectors, which noises arise because of' cathode emission variation, orVvariations in power supply voltages, the method essentially consistingin balancing out anode currents arising because of the said emissionvariations and simultaneously differentially varying'the path of anelectron stream between the cathode and anode by radio frequencycurrents to be detected in order to produce useful variation in anodeoutput. It is to be understood, of course, that the proportions of thetube may be made different from those shown in the figures, andfurthermore that the cylindrical electrodes need not be employed as theoutside envelope of the tube. l

Again, the tube may be arranged for regeneration from the output circuitback to the input circuit to increase its sensitivity as a detector.Thus, the employment of this new type of cathode ray tube as a detectorwhen employed with regeneration would make possible the successfuldevelopment of the super-regenerative type of receiver. The tube shouldbe relatively free from hum when alternating current is used on thefilament, so that it can t in well with recent developments ofalternating current operated rel ceivers.

While I have indicated and described several A systems for carrying myinvention into effect, it will be apparent to one skilled inthe art thatmy invention is by no means limited to the particularly organizationsshown and described, .but that many modifications in the circuitarrangements, as well as in the apparatus employed may be made withoutdeparting from the scope of my invention as set forth in thev appendedclaims. In particular, I wish to'pointout that the detailed proportions.and constructions of the cathode ray tube andr associated circuits shownwill undoubtedly be modied by careful considerations of detailed designand to permit of constructing the tube with less practical difficulties.

What I claim isz.. V1. A method of detecting modulated radio frequencycurrents whichV comprises emitting `a stream of electrons towards a pairof electrically balanced anodes, combining a stream at a mean .positionbetween a pair of differentially biased control electrodes, impressingmodulated radiofrequency energy upon the control electrodes, andelectrostatically shielding said anodes from said control electrodes.

2. A method of detecting radio frequency currents which comprisesprojecting a stream of electrons from a cathode towards a pair ofsymmetrically connected anodes,-maintaining the ow of the stream at amean position adjacent one or more control electrodes, impressingmodulated alternating current energy across an impedance" connectedbetween the cathode and control electrodes whereby one of said controlelectrodes is variably biased in accordance with said modulation, andutilizing said variable bias to deflect the stream from said meanposition whereby the currents to said anodes are differentially variedin correspondence to said modulation.

3. The method ofV detecting modulated high frequency currents whichcomprises projecting a stream of electrons between a pair of controlelectrodes, disposing a pair of symmetrically connected anodes in thepath of said stream, differentially biasing said control electrodes tomaintain the stream at a mean position between said electrodes, Y

vcal circuit connecting said anodes to said cathode,

means for tuning said circuit, an input circuit connected between one ofsaid control electrodes and said cathode, means for tuning said circuit,and means for maintaining each of said control electrodes at a differentdirect current potential with respect to said cathode.

5. Means for demodulating signal modulated currents including a cathoderay electron discharge device having a plurality of anodes, a pluralityof control electrodes, an emission element substantially equidistantfrom each of said anodes, and a screening electrode interposed betweensaid anodes and said cathode, a symmetrical circuit connecting saidanodes to said cathodes, `means for tuning said circuit, means for,k

potential to said screeningelectrode, an input circuit connecting one ofsaid= control electrodes to said cathode, and means for applyingdifferent direct current vpotentials to each of said control electrodes.l g

6L A demodulation device vincluding an emission element, a plurality oranodes equally spaced from said emission element, control electrodes, ascreen grid electrode interposed between said anodes and said cathode,an output circuit conv nected between said anodes, an input circuitconnected between said 'cathode and one `of said control electrodes, andmeans for applying equal direct current biasing potentials topeach ofsaid anodes andidiierent direct current biasing potentials tc each ofthe other electrodes.

7. Means for rectifying electrical oscillations includinga cathode-raytube having a plurality of anodes, a symmetrical output circuitVconnected between said anodes, a plurality of control electrodes, acathode, an input circuit connected between lone of saidcontrolelectrodes and said cathode, and a screen electrodeinterposedbetween said anodes and said cathode.

8. Means for dernodulatin'g electrical oscillations including a cathoderay electron discharge device having a plurality of anodes, apluralityof control electrodes and a cathode rincluding a symmetrical circuitconnecting said anodes to said cathode, means for tuning said circuit,an input circuit connected between one of said control electrodes andsaid cathode, means for tuning saidcircuit, means for maintaining eachof said control electrodes at a'diiferent direct currentv potential withrespect to said cathode, a screen electrode between said anodes and saidcathode, and means for applying a potential to said screen electrode. iY

9. Means for. demodulating sign-al modulated currents including `arcathode ray Vrelectron discharge device having a plurality oiv anodesaa plurality .of control electrodes, an emission Velement substantiallyequidistant from each of said anodes, and-a screening electrodeinterposed betweenv said ano-des and, said emission element, asymmetrical circuit connecting said anodes to said cathodes, means fortuning said circuit, means for` applying direct current potential tosaid anodes, means for applying a different direct current potential tosaid screening electrode, an input circuit connecting one of saidcontrol electrodes to said emission element, and means including animpedance in said input circuit for applying diff rent direct currentpotentials to each of said control electrodes.

l0, A thermionic demodulating device comprising an envelope including aplurality of anodes, a plurality of control electrodes, an' emissionelement spaced equidistant from each anode, means for applying directYcurrent potential to each anode, means for applying signals to vrsaiddemodulation device includingan input circuit including a tunedinductance connected Ybetween one of said control electrodes and, saidemission element, means for applying a diierent direct current potentialbetween each control electrode andl said emission element, means forcausing signal modulations in said input circuit to produce similarpotential changes on the anodes of said demodulator including animpedance connected between one of said control electrodes andYVWith-respect to said anodes, a cathode equidis- *tantV from each anode,a screening grid located between said control electrodes and saidanodes, a symmetrical circuit including atuning condenser connectedbetween said anodes, common tential to each of said anodes, means'forimpressing signal modulated oscillations between one of said controlelectrodes and said cathodeincluding an inductance and avariablecondenser, and means forV applying a diierent direct current potentialbetweeneachof said control electrodes and said cathode, and between saidscreening grid and said cathode. Y

l2.r A thermionic demodulatorV including a dis-V charge device having aplurality of anodes, a plurality'of control electrodes, and a cathode,means for' connecting said electrodes for grid rectiiication of thesignal including, means for applyingithe same direct current potentialbetween each anode and said cathode, a tunable repeater circuitsymmetrically connected between said anodes, means for impressing signaloscillations between one of said control electrodes and said cathode,means for applying different direct current potentials to said controlelectrodes and said cathode includingan impedance connected between oneof said control electrodes and said cathode, and a screenfelectrodeinterposed between said controlv electrodes and said anodes.

i3. A means of demodulating signals by a system including, a cathode`ray'tube having a cathode, a pair of controlielectrodes, a pair ofanodes, and a screen electrode between said control electrodes and saidanodes, which comprises energizing one of the control electrodes' ofsaid tube at-the frequency of the incoming signals, maintaining thecontrol electrodes of said .tubel at different direct currentpotentials, feeding theresultant energy from the anodes of said tubes inopposition, and maintaining said screen electrode at a positivepotential with respect to said cathode.

CLARENCE W. HANSELL.

.means for applying a similar direct current po-

